London: Planetary scientists have come up with a new theory on the size of black holes -- claiming some of them have no "table manners", and tip their "food" directly into their mouths, eating more than one course simultaneously.

For its research, a team from the University of Leicester in the UK and Monash University in Australia investigated how some black holes grow so fast that they are billions of times heavier than the sun.

Prof Andrew King at University of Leicester, who led the study, said: "Almost every galaxy has an enormously massive black hole in its centre. Our own galaxy, the Milky Way, has one about four million times heavier than the sun.

"But some galaxies have black holes a thousand times heavier still. We know they grew very quickly after the Big Bang. These hugely massive black holes were already full-grown when the universe was very young, less than a tenth of its present age."

Black holes grow by sucking in gas. This forms a disc around the hole and spirals in, but usually so slowly that the holes could not have grown to these huge masses in the entire age of the universe.

The scientists made a computer simulation of two gas discs orbiting a black hole at different angles. After a short time the discs spread and collide, and large amounts of gas fall into the hole. According to their calculations black holes can grow 1,000 times faster when this happens.

"If two guys ride motorbikes on a Wall of Death and they collide, they lose the centrifugal force holding them to the walls and fall," says King. The same thing happens to the gas in these discs, and it falls in towards the hole.

This may explain how these black holes got so big so fast. "We don`t know exactly how gas flows inside galaxies in the early universe but I think it`s very promising that if the
flows are chaotic it is very easy for the black hole to feed," said King.

The findings are to be published in the `Monthly Notices of the Royal Astronomical Society`.